The present invention relates to an improvement in a drive mechanism for use in an industrial robot, and more particularly to a drive mechanism for a wrist manipulator.
A typical prior art mechanism of such type will be described with reference to FIGS. 1 to 3. In FIGS. 1 to 3, there is schematically shown the prior art mechanism which comprises a first servo motor 101, a second servo motor 102, a third servo motor 103, a pulley 104 secured to an output shaft of the first servo motor 101, a transmission belt 105 for transmitting a rotational torque from the pulley 104 to a pulley 106, a box-shaped casing 107, a pulley 108 secured to an output shaft of the second servo motor 102, a transmission belt 109 for transmitting a rotational torque from the pulley 108 to a pulley 110, a box-shaped casing 162, a pulley 111 (FIG. 2) secured to an output shaft of the third servo motor 103, a transmission belt 112 for transmitting a rotational torque from the pulley 111 to a pulley 113, a box-shaped casing 163, bevel gears 114 and 116 secured to the pulleys 106 and 110, respectively, other bevel gears 115 and 117 engaging with the bevel gears 114 and 116, respectively, bearings 118, 119 and 120, 121 for rotatingly supporting the pulley 106, bevel gear 114 and pulley 110, bevel gear 116, respectively, drive shafts 126, 127 and 128 for transmitting the rotational torques of the bevel gears 115 and 116 and the pulley 113, respectively, bearings 122, 123 and 133 for supporting the drive shaft 128, bearings 124, 132 and 125, 134 for supporting the drive shafts 126 and 127, respectively, a second link 131 surrounding the drive shafts 126, 127 and 128 and the like, bearings 129 and 130 for supporting the second link 131, a first link 164 (best shown in FIG. 3) supporting at one end the second link 131, a first box 165 securing an inwardly toothed gear 137 later described, a bearing 135 for rotatably supporting the first box 165, a spur gear 136 secured to the drive shaft 126, the inwardly toothed gear 137 being meshed with the spur gear 136, a spur gear 138 secured to the drive shaft 127, a tubular spur gear 139 meshing with the spur gear 138, a bevel gear 140 secured to the spur gear 139, bearings 141 and 142 supporting the spur gear 139 and the bevel gear 140, a bevel gear 143 engaging with the bevel gear 140, a pulley 148 secured to a boss portion 143' of the bevel gear 143, bearings 144 and 145 supporting the bevel gear 143 and the pulley 148, a bevel gear 146 secured to the drive shaft 128, a bevel gear 147 meshing with the bevel gear 146, a transmission belt 149 for transmitting a rotational torque from the pulley 148 to a pulley 150, a pulley 151 secured to the boss portion of the bevel gear 147, a transmission belt 152 for transmitting a rotational torque from the pulley 151 to a pulley 153, a second box 166 fixed to the boss portion of the pulley 150, bearings 156 and 157 supporting the pulley 150 and the second box 166, a bevel gear 158 secured to the pulley 153, a bevel gear 159 engaging with the bevel gear 158, an output shaft 159a secured to the bevel gear 159, bearings 160 and 161 for rotatably supporting the bevel gear 159 and the output shaft 159a, bearings 154 and 155 for supporting the pulley 153 and the bevel gear 158, and bearing 167 for supporting the second box 166. A first device is composed of the spur gear 136, the inwardly toothed gear 137, the first box 165 and the like. A second device is composed of the spur gears 138, 139, the bevel gears 140, 143, the pulleys 148, 150, the second box 166 and the like. A third device is composed of the bevel gears 146, 147, the pulleys 151, 153, the bevel gears 158, 159, the output shaft 159a, and the like. It should be noted that a rotary axis of the first box 165 of the first device is perpendicular to a rotary axis of the second box 166 of the second device, and the rotary axis of the second box 166 of the second device is perpendicular to a rotary axis of the output shaft 159a of the third device.
In operation, a rotational torque of the first servo motor 101 is transmitted to the drive shaft 126 through gradual reduction in rotational speed and axis-conversion by the pulleys 104, 106 and the bevel gears 114, 115, and the rotation is further decreased in speed by the spur gear 136 and the inwardly toothed gear 137 to cause the first box 165 to rotate. The first device thus operates. Similarly, a rotational torque of the second servo motor 102 is transmitted to the drive shaft 127 through gradual reduction in rotational speed and axis-conversion by the pulleys 108, 110 and the bevel gears 116, 117 and the rotation is further decreased in speed and changed in rotary axial direction by the spur gears 138, 139 and the bevel gears 140, 143 to rotate the second box 166 through the pulleys 148, 150. The second device thus operates. A rotational torque of the third servo motor 103 is reduced in speed through the pulleys 111, 113 and is transmitted to the drive shaft 128. The rotation is gradually reduced in speed and changed in rotary axial direction through the bevel gears 146, 147 and the pulleys 151, 153 and the bevel gears 158, 159 to thereby achieve the operation of the third device. The axes of rotation of the first and second devices are perpendicular to each other and the axes of rotation of the second and third devices are also perpendicular to each other. With the operation of the first through third devices, an end work effector (not shown) mounted on the output shaft 159a may achieve a so-called "wrist" operation of three degrees of freedom.
Moreover, referring to FIG. 3, rotation of a fourth servo motor 168 causes the second link 131 to rotate through a fourth link 171 and a third link 170. By the operation of the second link 131 and the first link 164 drivingly actuated by the fourth and fifth servo motors 168, 169 and the operation of the above-described wrist mechanism, the industrial robot may manipulate in five degrees of freedom.
In the manipulating system, the rotary axis of the first device composed of the spur gear 136, the inwardly toothed gear 137, the first box 165 and the like intersects at a right angle with the rotary axis of the second device composed of the spur gears 138, 139, the bevel gears 140, 143, the pulleys 148, 150, the second box 166 and the like, and also, the rotary axis of the second device intersects at a right angle with the rotary axis of the third device composed of the bevel gears 146, 147, the pulleys 151, 153 the bevel gears 158, 159, the output shaft 159a and the like. To obtain the three degrees of freedom, a number of mechanical components such as pulleys, spur gears, bevel gears and bearings are required. As a result, the number of mechanical components is increased. In addition, there is a great fear that the overall accuracy would deteriorate due to the addition of physical errors of the respective components. The mechanism of the wrist section is complicated and is heavy in weight. Thus, a mechanical strength of each link supporting the wrist section has to be increased, which leads to the enlargement of the overall system.